Radio frequency power amplifiers are used in numerous wireless communication applications. Many of these applications are in the field of consumer electronics, which are portable and require batteries. Although battery technology has advanced significantly in recent years, battery powered communication devices require maximum power efficiency for transmission of RF signals while using as little energy as possible.
Current wireless systems have increasing power amplifier linearity requirements to minimize adjacent and alternate channel distortion. A commonly applied technique to improve the linearity of RF power amplifiers is to increase their quiescent current so that the transistors forming the amplifier operate in a more linear portion of the current-to-voltage (i/v) curve. Unfortunately, increasing the quiescent current of the amplifier requires the amplifier to constantly operate at a high idle current even when small input signals do not demand the same linearity as larger inputs. Thus, there is a need for a bias current control technique that automatically adjusts bias currents based on the effective magnitude of the input signal being amplified to meet linearity requirements as well as maximize operating efficiency.